1. Technical Field
The present invention relates to electrosurgical pencils and, more particularly, to electrosurgical pencils carrying electrical switches for controlling application of command signals to electrosurgical generators.
2. Discussion of the Prior Art
Electrosurgical techniques have become widely used by surgeons in recent years. Accordingly, a need has developed for equipment that is easy to handle and operate, reliable and safe. Electrosurgical equipment normally includes a generator providing high frequency electrical cutting and coagulation signals for application to an electrode mounted in a handle, the latter electrode and handle combination being referred to herein as a pencil. The pencil is preferably long and slender so as to be held by the surgeon during surgery in the manner of a writing implement. In order to permit the surgeon to control the high frequency signals supplied to the electrode (for example, a continuous a.c. signal for cutting, or a pulse a.c. signal for coagulation), switches are mounted on the pencil and are selectively actuable to control application of command signals to the electrosurgical generator. In this manner, the switches permit selective generation of the cut and coagulation signals. The switches, of course, must be sealed to prevent intrusion of fluids and other contaminants into the pencil interior, and must be completely reliable to assure proper operation of concomitant precision and safety.
While there have been many attempts to produce electrosurgical pencils with finger-operated switches, there remains room for considerable improvement to increase durability and to assure proper and reliable switching operation at all times during use of the pencil. It is to this purpose that the present invention is directed.
Examples of prior art electrosurgical pencils are described and illustrated in the following U.S. patents: U.S. Pat. Nos. 3,911,241 (Garrard); 4,021,630 (Taylor); 4,032,738 (Esty et al); 4,034,761 (Prater et al); 4,112,950 (Pike); 4,170,234 (Graham); and 4,289,943 (Sadao).
The Taylor patent discloses a resilient contact switch formed of a flexible cap having an arcuate dome and a cylindrical upstanding sidewall. The sidewall is positioned to be sealed within a sleeve in the pencil housing by virtue of the cap being larger than the sleeve bore, thereby resulting in radial compression of the sidewall. A plunger extends inwardly from the dome to permit selective deflection of a concave metal plate at the distal end of the plunger to establish a connection contact between contacts on a circuit board. In a second embodiment disclosed in the Taylor patent, a conductive material can be used for the plunger, or a conductive plate may be bonded to the lower surface of the plunger.
The Esty et al patent discloses a generally flat electrosurgical pencil providing electrical interface between an electrosurgical signal generator and an exposed surgical electrode. Esty et al expressly state that the resilient contact switch of the Taylor patent could be used with the Esty et al pencil. The flat, elongated configuration of the housing of the Esty et al pencil is designed to approximate the flat handle feel of previous passive surgical instruments. A bore extending through one of the flat rigid surfaces comprising the pencil housing is outwardly encircled by an upright cylindrical wall terminating in inwardly turned shoulders. A momentary switch assembly includes a hollow peripheral sidewall retained in sealing engagement internal to the housing bore and the upright cylinder wall, and a cap having a cross section which is outwardly arcuate. Important aspects of the Esty et al pencil are the flexible cap with cylindrical sidewalls retained in sealed abutting engagement within the collar of the housing opening, and a closure extending across the sidewalls and having an external arcuate cross section.
The sidewall sealing arrangement required for the switch disclosed in both the Taylor and Esty et al patents is effective for sealing; however, the switch presents problems during fabrication. Specifically, the outside diameter of the sidewalls of the resilient member and the inside diameter of the receiving bore must be such that a tight seal is effected; however, if the fit between the two is too tight, it becomes extremely difficult to insert the resilient member into the bore during assembly of the unit.
In addition to the foregoing, prior art electrosurgical pencil switches, when used in conjunction with printed circuit boards, tend to be unreliable. Specifically, an oxidized film inherently forms on all metallic switch contacts on printed circuit boards. When a movable metallic surface is used to selectively bridge such contacts, the oxidized film often prevents good electrical connection between the movable surface and the circuit board contacts, thereby preventing the desired circuit closure.